Reverse-jet type dust filter



April 6, 1965 c.s.scHu| 1-z ETAL 3,176,449

REVERSE-JET TYPE DUST FILTER "i5, www.

April 6, 1965 l c. s. scHuLTz ETAL 3,176,449

REVERSE-JET TYPE DUST FILTER Filed DSC. 6, 1961 4 Sheets-Sheet 2 BYG. Q Pavn@ April 6, 1965 c. s. scHuLrz ETAL 3,176,449

REVERSE-JET TYPE DUST FILTER Filed Dec. 6, 1961 4 Sheets-Sheet 3 INVENTORS CAI/na s. SCHULTZ, faogr J. w. WJLLJAWS.

April 6, 1965 c. s. scHULTz ETAL 3,176,449

REVERSE-JET TYPE DUST FILTER 4 Sheets-Sheet 4 Filed Deo. 6, 1961 INVENTORS. GCMLOS s. scf/0L Tz, ROBERT J. M WIL 41ans.

oggi@ @406,001

@arles S. Schultz, Baltimore, and Robert W. Wiiliams,

Lutherville, Md., assignors, by mesne assignments, to

lualo Forge @omni-my, Einhalt), NFL, a corporation ot' New Yer-lk Filed Dec. 6y ll, Ser. No. lov/9334 l@ Claims. (Cl. 55u-2%) This invention relates to an improved apparatus for cleaning the medium employed for littering dust-laden gases, the cleaning being effected without interruption of the filtering operation by blowing a jet ot relatively highpressure gas through the iilter medium in a direction reverse to the flow oi the gas being ltered.

More particularly, the invention relates to an improvement of the mechanism for reciprocating the reverse-jet cleaning device relative to the rilter medium and to means for controlling the extent oi physical contact between the cleaning device and the iilter medium.

It is therefore an object of the present invention to provide apparatus for greatly increasing the speed of the reverse-iet cleaning device on the up stroke thereby providing an increase in cleaning eiiciency and, as a result thereof, an increase in the filtering efficiency for the same period of operation of the reVersejet.

Another object of the present invention is to provide apparatus to so position the reverse-jet cleaning device as to eliminate physical contact between the device and the filter medium throughout the up stroke and then to reposition the device for the conventional down stroke during which the device remains in contact with the lilter medium.

A further object of the present invention is the provision of apparat-us for greatly increasing the speed of movement of the reverse-iet cleaning device during the up stroke relative to the speed thereof during the down stroke whereby equivalent filter etliciency may be provided with decreased reverse-jet on time.

According to the present invention mechanism for reciprocating the blow ring which encircles the cylindrical rilter medium or bag is provided comprising means for moving the blow ring to a retracted position out of physical Contact with the filter bag, means for moving the blow ring upward at a sneed much greater than the conventional speed of the up stroke, means elective at the end of the up stroke for returning the blow ring into Contact with the bag for the relatively slow-speed down stroke and means for controlling the movement of the blow ring in the downward direction during the down stroke in response to tie pressure drop of the gases passing from inside to outside of the bag.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIGURE l is a schematic representation of the operating mechanism for controlling the vertical reciprocation of the blow ring,

FIGURE 2 is an isometric view of the preferred embodiment of the blow ring retraction device with the blow ring segments shown in retracted position for the up stroke,

FlGURE 3 is an isometric View or the pret-erred ernbodi'of the blow ring retraction device -with the blow ring the blow ring retraction device,

gUnited States Patent O ice FGURE 5 is an elevational View of the second embodiment of the blow ring retraction device positioned in the bag engaging position employed during the down stroke and FiGURE 6 is an elevational View of the second embodiment of the blow ring retraction device positioned the retracted position employed during the up stroke.

Reference to FGURE l shows a cylindrical cloth filtering element or filter bag lil into the top of which dustladen gases are introduced through a pipe 12 or, in the case or multiple filter elements through a manifold. The dust-laden gas moves down through filter bag l1 and, due to the elevated pressure of this gas, it passes out through the fabric or the ilter bag 1l from inside to outside. luring the passage of this gas from inside to outside ilter bag il a large percentage of the dust particles entrained therein are removed from the gas and remain in lilter bag 1l.

Along the outer periphery of filter bag l1 a carriage 13 is mounted for movement in a vertically reciprocating fashion. Mounted on carriage i3 is blow ring 14 which comprises a pair of semi-circular tubular, slotted segments i6 and l? which in their effective blowing position Contact the filter bag il depressing the bag inwardly to a slight degree at the point of contact. Blow ring elements i6 and 17 are provided with air under pressure by means of flexible pipes l and 19 and this air, after distribution to segments lo and 17, is discharged through elongated orifices or slots 2l and 23 which slots extend substantially throughout the length of the inner surface i blow ring segments lr6 and i7. This air being under pressure passes into the interior of lter bag ll through the fabric thereof dislodging the dust particles from within the fabric and from the inner surface of filter bag 1l. The dislodged dust particles then settle into hopper 23 from which they may be removed for appropriate disposition.

This action of blow ring 14 is cleaning iilter bag 11 during its reciprocating action up and down outside bag ll is calle reverse-jet action. The initiation or discontinuance of this action is controlled by pressure switch 2d. As more and more dust particles are deposited on the inside of lter bag lll, the bag eventually becomes so thoroughly coated that the pressure drop of the gas as it gasses through the bag from inside to outside becomes greater and greater. When it reaches a predetermined level, pressure switch 24 will make close electrical contacts therein (not shown) and start both reverse iet-blower 2e and twospeed reversible motor 27. Pressure switches able to serve in this capacity are commcrcially available, therefore additional description of pressure switch 3d would be superfluous.

As carriage i3 continues on its downward path the high pressure cleaning air supplied by blower 25 passes through hose VZS into manifold Zh in blow ring carriage 13 whence it is distributed to blow ring elements 16 and i7 through air supply pipes 18 and i9.

The cleaning air in forcing its way from without to within iilter bag lll docs two things. First, it keeps open a suidcient number of the passageways through the fabric to maintain the desired degree of porosity. Second, it either breaks oil the dust layer on the inner surface of the fabric or at least forces it to separate from the fabric suliiciently to open channels therebetween to permit the air being filtered to .flow into the fabric itself.

When the pressure or" the air within filter bag 11 drops hlldfiil) E .2 During the down stroke of the blow ring the carriage `may be stopped and restarted two or three times during typical operation.' It has been determined that on Vthe .up stroke, on the contrary, regardless of the speed under most v, operating conditions the vreverse-jet system isV unable to clean lter bag 11 well enough to cause pressure drop through the bag to be reduced to the prescribed 41/2 inches of water required to actuate pressure switch 24 and stopthe reverse-jet action.

These development'rtests have confirmed the fact that eliective than Vduring the up stroke over a wide range of flow ring travel speeds (20 to 70 feet per minute) .Y Y

This is not to say, however, that the up stroke is totally ineffective; Tests have also shown that turning oii the reverse-jet air during the up stroke results in higher average pressure drops through the iilter medium Vthan Y reverse-jet action during the down stroke is much more f Occur whenreverse-jet action is used on the up strokeV Y thereby indicating a decrease inrlter performance'.

. The following 'table shows the results of testing kwherein the ow of dust-laden gas through the lter was adjusted so that the reverse-jet action was called for by pressure switch 24 during approximately 30% of the total filter operating time. Since the reverse-jet .action did not stop during the up stroke, the reversevjet action remained on for 100%of each up strolce. In contrast thereto` fthe reverse-jet' action was stopped several times during each ydown stroke with the result that the reverse-jet y on time during this stroke amounted to a relatively Vsmall percentage of the period required to completethe down stroke. Y

Asa result of the above ftests it wasrestablished that the up V'stroke has Va detrimental ielect on the overall filter performance, since it increa-ses Athe total averageV reverse-jet ,on time. h Y Y 'In order to optimize this condition the present invenaire/ias ute used during the up stroke, the pressure differential through the wall of iilter bag 11 increases to a very high level when reverse-jet cleaning is not used on the up stroke.

Since the cost of lter bags is very high, this improvement designed to increase the useful life of filter bags by eliminating physical Contact between blow ring'14 and bag 11 will produce substantial savings in operating costs.

The apparatus for reciprocating blow ring carriage 13 in accordance with the present invention' comprises conventional torsion shaft 31 from Whichis suspended blow ear-y riage 13 and counterweight 32 by means of chains 33 and 34 and pulleys 36 and 37. Shaft 31 is rotatably driven through sprocket 38 and chain 39 by shaft 41 supported in suitable bearings. Rotary limit switch 42, type GSI-Z-l (made by the Allen Bradley Company) is also driven by shaft 41 through -a sprocketchain combination 43 and serves to actuate electrical contacts at the top and at the bottom of the; blow ring reciprocating strokes.

Shaft 41 is driven through a `V-belt drive system by twospeed, reversible electric motor 27.' Dur-ing the down stroke motor 27 operates at its low speed and drives shaft 41 via sheaves 44 and 46, belt 47 and two-directional clutch 48. A suitable two-directional clutch is the' REV-y `LOK clutch manufactured by Form Sprag Company of Warren, Michigan. TheY clutch 49 is'of the conventional overrunningvariety and overruns freely in this direction ofrotation.

At `the' end of the low speed ,down stroke, motor 27 is reversedr by reversing controller 51 in response to a signal from rotary'limitrswitch 42. For the high speed upfstroke motor 27 runs at high speed and drives shaftl 41 via sheave 52,b1elt 53, sheave 54,l overrunnin'g clutch -Vdir'cctionl TheV outer-race of two-directional clutch 48 overruns freely and shaft 55 drives shaft 41 'through the inner clutch portion. By properlyselecting the motor speeds and the sheave sizesY the desired speed forV downward travel and the highest speed for be obtained.. Y

In addition to providing the above-*described change upward travel of'carriage 13 may Y in directionrand change in speed of reciprocatpion at the ends of Ythe up and the down strokes, retraction device V56 is provided for moving the blow ring segments 16 and 17 either into retracted position or into physical'contact tionprovides for aretu'rn'greatly increasing the blow ring travel speed on'the .up stroke thereby transferring Vto the more etiici'ent downV stroke more of the less; eiii-l cient reverse-jetpcleaning time conventionally expended during the up stroke.

` Atl the same time, both to facilitate a higher speed re-Y turn and to produ the added advantage of decreased bag Wear the blowV ring segments 16 yand 17 lare moved to a vretracted position at the'bottom-of the down stroke`V ,Y remaining in thisretracted position until the blow ring 14V y reaches thetopcf thegfu'p? stroke. Y. .v Y n As a result of 4the decreasedperiod of contact between blowl ring segments 16and 17 and filter bag 11'ar1d,"i:`u1fV ther, as a result of the' ldecreased reverse-jetfon time,v I bag wear will be reduced by a factor ofA about .'Th'eoetically, it would be desirable Vto increase the Vup stroke speed to an intinitelygrea-t value, however, this is presently infeasible' andthe highest V'practical speed must be de with tilterbag 11 as required. 1

As is shown in FIGURES 2 and.3,Cam 57 slidably Vmounted on carriage 13 in conjunctionrwith suitable guide means serves to move segments 16 andV 17 into the retracted position or to permit springs.' 58 and 59r mounted Y on support rod tl'to bias'segmentsfl and 17 inwardly 'i untilrsupport amis 61 and 62`movable along rod tl'reach snap lock rings 6?l and 64. A Vduplicate retraction device 56,1not shown,V is provided diametrically opposite the rements 16 and 17 'Y traction device shown to vact uponrthe otherrends of seg- FIGUREV 2 shows end of the down stroke preparatory to the execution koffthe'highY Vspeed upwstroke Asshown cam 57. is

. slideably mounted on carriage/.13 for lfree movement up and down relative thereto with limitations on the sidewardmovement of-cam 57 being imposedA by camguide pin velopedfor each device. The minimum valuev for' the up stroke. speed isabout-twice Ithe speed of the downl stroke or feet per minute' whichever has the greater p value..

If vthe-.speed during thefup' stroke is high enough, the increase. in the pressure differential. through' theV wall of filter bag 11'during this strokev due to the lackV of reverse@ jet cleaning 'actionkgwill be very smalh WithY conventionalY low travel speeds inthe orderrof` 30 tof4tlfeet perV min- 79 VVdownward movement of Ycam 57 ceases, but carriage13 l continues to'move in 4a'downward direction to complete Y-r its stroke. Y Thecarriage- 13 movesdown-relative to vcamY 57Y and the portions? of guide lugs 66 and 67 at the Vbot- 68 in vertical slot 69'and guide slots70, 71, 72V and 73 in bifurcated guide lugs 66 and 67. Y

- When carriage lt3 is close'to theV bottom of its down stroke, the cam 57. strikes the floor 74 of Athe'iilter unit as'shown or some other Xed object. Therefore, the

tomr'o'fY guide slots V72 an'd73 strike the inclined edges p the position in which earn l57- isV V,placed relative toibifurcate'd guide lugs 66 vand 67 Vat the 60.

3,1 vente 76 and 77 and cam 57 riding therealong during the continued downward movement of carriage i3.

Segments 16 and ll7 are gradually forced apart against the biasing force of springs 58, 59 as guide lugs 66 and 67 ride down inclined edges 76 and 77 until the bifurcated guide lugs 66 and 67 pass over shoulders 78 and 79, move inwardly toward each other against the wide shank Si of cam 57 and into the retracted position. As shown, wide shank 8l is slightiy narrower than the distance between shoulders 78 and 7%.

However, the width of wide shank Si is sufficiently large so that retraction device 56 holds the blow ring Segments 16 and i7 spaced apart from each other sufficiently far so that these segments would be out of physical contact with the largest standard bag ti. This consideration is necessary, since iilter bags vary slightly in size when in use due to fabrication errors, the pressure within the bag, actual bag construction and the operating environment.

The elements of retraction device 56 retain their relative positions throughout the high speed up stroke until carriage 13 nears the top of its stroke, since wide shank 81 prevents springs 5S and S9 from moving segments i6 and i7 closer together and since the wider dimension between shoulders 78 and 79 prevents cam 57 from dropping under the force of gravity.

As the carriage nears the end of the up stroke, cam '7 strikes the ceiling 82 ot the filter, or other fixed object, whereby upward movement of cam 57 is immediately halted. Carriage i3, however, continues to move up to complete its stroke and in so doing bifurcated guide lugs 66 and 67 are forced away from each other against the force of springs 5S, 59 and then up relative to cam 57 aiong inclined sides 83 and Se of cam 57 until these guide lugs have passed shoulders 7S and '79.

From this point on, guide lugs 66 and 67 (and thereby segments t6 and i7) move toward each other along sloping edges 76 and 77 under the bias of springs 5S and 59 until support arms 6i and 62 contact snap iock rings 63 and 64 fixing the inside diameter of blow ring M. In this position guide lugs 65 and 67 remain far enough apart so as not to contact narrow shank d6 or receive any portion thereof within guide slots 7), 7l, 72 or 73. Cam 57 will, of course, move down under the inluence of gravity until cam guide pin 63 reaches the upper end of vertical slot 69. With the several elements of retraction device 56 in the relative positions as shown in FIGURE 3, blow ring segments i5 and 17 are placed in physical contact with lter bag lli preparatory to executing the slow speed down stroke to clean collected dust from the inner surface and interstiees of the fabric of filter bag il in the conventional manner.

A second embodiment of the retraction device employed in the present invention is shown in FEGURES 4, 5 and 6. Here the retraction device itil consists of a cam 192 of modified configuration trom that disclosed in the preferred embodiment together with a different means for guiding the vertical movement of cam M32..

Blow ring 193 is of the self-adjusting type with lugs 104 and itin formed integral with blow ring segments 167 and M33. In this arrangement, blow ring segments 1597 and MES are biased inwardly into physical contact with filter bag t by springs 11i. The mechanism for positioning blow ring segments im' and 16S relative to carriage 1.?13 are well known and are indicated schematically as the pivotal connections 1.2M and M6.

Compressed air from a blower, such as the blower 26 in FIGURE l, passed through hoses i' and M3 into manifolds 115.9 and lll in the blow ring carriage 313 from whence this air is distributed to blow ring segments i307 and S through air supply tubing H22, 123, ft2- and 126 from whence it is ejected through slots (not shown) similar to slots 2i and 22 in the preferred embodiment and in the manner described in connection therewith.

Since FIGURE 4 is a plan view of blow ring 193 and carriage H3 the relative positioning of the two lretraction @i devices i551, lill diametrically opposed relative to filter bag M39 is clearly shown. Similar relative positioning is employed in the case of retraction devices 56, 56 in the preferred embodiment.

The cleaning operation employing retraction device tot is identical to the operation of the preferred embodiment and these embodiments differ only in structural detail. Near the bottom of the down stroke, cam 102 strikes the bottom 127 of the lter assembly or some other soiid abutment to prevent further downward motion of cam 192. Blow ring carriage M3 and blow ring segments 197 and 1b@ mounted thereon continue to move downwardly to complete the down stroke. Lugs 1M' 3.96 strike inclined surfaces and 29 and are moved further and further apart against the force of springs iii, iii as blow ring segments i637 and NS are moved downwardly relative to cam to2. As soon as lugs los and idd have passed shoulders il. and E32, continued downward motion of blow ring segments HB7 and tot; cause lugs and itin to move inwardly along inclined surfaces and i3d until they rest against wide shank 136 of cam to2. In this position, blow ring segments 97 and No re retracted from physical contact with iilter bag iti@ and remain so retracted during the high speed up stroke.

Near the end of tie up stroke of carriage 13 and blow ring lt as shown in FIGURE 6, narrow shank 37 forming the upper end of cam N2 strikes the ceiling 133 of the filter device or some other abutment. Carriage M3 in its continued upward motion forces lugs 104 and Title to ride up inclined surfaces T133 and 134;, past shoulders 131 and i3?. and toward each other along inclined surfaces t28 and 129 under the force ot springs ill and i2 until these lugs reach a position relative to narrow shank 37 such as is shown in FIGURE 5.' ln this posi tion segments W7 and 1% are urged into physical contact with bag iii@ by springs itil, ill as shown in FIG- URE 4 for the slow speed down stroke.

Since cam MP2 is no longer supported by lugs lo@ and idd as shown in the position shown in FEGURE 6, provision must be made to prevent cam i102 from falling to an inaccessible position. Also, provision must be made to properly align cam lidi for its vertical motion relative to carriage 113. These ends are achieved by providing reduced portion l??? of cam lo?. and arranging this reduced portion 139 to pass through a slot bounded by member Ml, spacers L42 and M3 (shown in cutaway portions of FGURE 4) and framing member 144 forming part of carriage 113. By these expedients movement of cam 192 is limited to vertical movement relative to carriage M3 with shoulders 146 and 147 preventing cam NZ from dropping out of the device.

Springs til, iii must be properly selected to provide suitable positioning of self-adjusting blow rings segments m7 and 168 in physical contact with bag 15,29 for the down stroke, blow ring segments M7 and lili; being so positioned by springs `11?., 111 that these segments are forced into goed contact with lter bag 14.29 without contact between lugs Jiri, i496 and narrow Shank 137 of cam llZ.

Obviously many modications of the present invent-ion ar-e possible in the light of the above teachings. It is therefore to be understood, that within the scope of the amended claims, the invention may be practiced otherwise than as specilically described.

We claim:

1. In a dust lter wherein a porous, iieX-ible, cylindrical iilter medium is employed for accumulating upon the inner side thereof solid particles from a ldust-laden gas and whenein a reverse-jet cleanirrl.7 device comprising a plurmity of separate hollow curved sections mounted on a carriage and substantially :encircling the lter medium is employed to dislodge the solid particles from the iilter medium by ejecting a jet of pressurized iluid from withoutt-o within said filter medium .through antoriiice in each curved section While the reverse-jetY cleaning device is reciprocated along the length VIVof the flter'medium, the improvement comprising means mounted on the carriage for moving said plurality of curved sections ,to `a retr-acted position out Iof physical contact with said filter medium and means connected to said Ireverse-jet cleaningdevice for reciprocating' said reverse-'jet cleaning device with a Vhigh speed up stroke and a low speed do-wn stroke.

2. In a dust lter the combination of a porous, flexible, cylindrical-lter medium for .accumulating uponfthe inner side thereof solid particles from .a dust-laden gas, a reurging said sectionsyinto yielding engagement with the outer side-of said iilter medium on the down, stroke, each kof said sections having an orioe therein in position to direct a jet of Ypressurized `fluid through said filter me- Y dium to dislodge accumulated solids from said'inner side,

motor Ameans connected :tosaid reversesj-et cleaning device for reciprocating said reverse-jet cleaning device relative to said vfilter medium -at high speed on the up 1 str-oke and at low speed on the down stroke, pressureverse-jet cleaning `device substantially encircling said 'filter` medium comprising a plurality of separate hollow curved sections independently urge-d into normalworking posif tion iu yielding engagement with the Youter side ofYsa-id lter medium on the down stroke, each of s-aid sections Y having an orifice located inl its inner periphery to'direct a jet of pressurized fluid through said filter medium to dislodge accumulated solids from said inner side, means consensitive means connected'to said motor means land in communication with the zone within the filter medium for Yenergizing land deenergizing said motor means Vin response to changes in pressure within said zone, .an elongatedmember ymounted on said carriage and vertically movable; relative thereto, abutment portions formed on said curved sections in juxtaposition with said elongated Y Y member; `first means `formed on said elongated member nected to said reverse-jet `cleaning device for reciprocating said reverse-jet cleaning device relative to said ilterrmedium at high speed on the up stroke and at low speed on the down stroke Vandmeans for retracting said plurality of curved sections fromsaid normal Working posi-fY tion for the up stroke.

3. In a dust lter, the combination set -forth in claim 2, wherein thesretracting means comp-rises 4'an elongatedieam supported on the reverse-jet cleaning device for vertical movement relative thereto. yand guide means formed on the curved sections adjacentV said cam, said guide means and said elongated cam being in juxtaposition.Y t

4. In a dust iltenthe combination set forth in claim 2 wherein the retracting means comprises an elongated cam supported on the reverse-jet cleaning device 4for verticalmovement relative thereto, guide means mounted on said reVerse-jetcleaning ydevice and engaging Asaid cam` and- Yabutting means formed on Vthe curved'sections adjacent saidcarn.` 4

5. In a dust iilter theV combination of aporousv flexible Y cylindrical filter, medium for accumulating upon the inner side thereof solid particles from Ia dust-laden gas, aV reverse-jet cleaning device vsubstantially encircling said lilter medium comprising a plurality of separate hollow' curved sections mounted on a carriage, means for independently urging said sections intoV yielding engagement withlthe outer sideV of said iilter medium on the down7 stroke, n each of said sections having an orifice therein` in position to direct aY jet of pressurized uid through said filter Vme-r dium to dislodge accumulated solids *from said inner side, means connectedto said reverse-jet cleaning device'V for reciprocating'said'reversej-et rcleaning device relative to said filter medium at high speed on the up strokerandat f low speed on Ythe downstr'oke, elongated member mounted on said carriage Vand vertically movable relativef thereto, abutment portions formed Aon said curved sections in juxtaposition -With said elongated member, irst means formed on said elongated member for coacting with said f abutment portionsrto retract said. pluralityof curved sections to a position out ofV physical contact with said Afilter for coacting'with said abutment portions to retract said plurality of curved sections to' a position out of physical contact with said filter medium against the force of said urging means at the' end Aof the down stroke, second means formed onY said elongated member for coacting withY said abutment member to retain said plurality of curved .sections in retracted position dur-ing the up stroke and third means formed on said elongated member vfor releasing said plu'ajality-V of curved sections from the retracted position at the end o'fthe up stroke.

7. vIn a dust ilterthccombination of a porous flexible hollow elongated iilter medium for accumulating on the inner side thereof solid particles-from a dust laden gas, a

reverse jet cleaning device located'proximate the outer g surface Yof Vsaid elongated iilter medium and including ya plurality` of hollow sections,V means locating said hollow sections in a rst spaced relationship to provide anormaljworking position-relative to said outersurface of said elongated filter medium, means for supplying said pressurized fluid to said hollow sections, said hollow sections having oriiices 4rfory directing jets of pressurized fluid to- Ward said outer surface of said elongated iilter medium to vsaid ex'ibl'e hollow elongated fil-ter medium-during travel of said hollow sections in saidopp'osite direction. f

8.- In a dust iiltertlie combination of a porous flexible' elongated [filter medium' having an' inner surface for ac' medium against the Iforce ofY said urging means at' theiendv Y of the fdown" strokegrsecond means formedon said elonf gated memberfor coacting with said abutment member to ,retain said plurality, of curved sections in retracted-posif tion during the'fup stroke and third meansY formed on saidy elongated member'for coacting with'said abutmentVV means to release said plurality of curved sections vfrom the 4 retracted position .at the` end ofthe up stroke.'

6, In a dust filter the combination of a porous flexible cylindrical Afilter mediumY for accumulating uponvthe innerv side thereof solid particlcsftfrom aV dustfladen'gas, laffe i verse-jet cleaning devicesubstantially encircling said filterY sections mountedon a carriage,means'for'.independently rmedium comprsing'a plurality .of separate hollow curved cumulating solid particles thereon froml a dust laden gas v and an outer, surface on the opposite side of said filter me-z dium vfrom Vsaid inner surface, a reverse,Y jet cleaningdevice including hollow section means, vmeans locating said hollow'section'rrneans in a Afirst position relative to said v outer surface yof saidfiilter mediumto providea'normal working position,means for supplying pressurized fluidv toV said hollow section means, oriiice means in Vsaid hollow section means for directing .a jet of pressurized fluid toward said outer' surface of said elongated'ilter medium to dislodge said 'accumulated' s-olids from said'inner sur-V VKface while. said` hollow section means is in said normal' working position, means connected to said reverse jet cleaning device for moving,v said ,hollow section means I along said outer surface of said elongated lter medium ASat Va lov;7 `speed in oncdirectionwhen said hollowsection means is intsaid normal Working-p'ositionand'v at a high lspeed sin the opposite direction, and means for causing said hollow section means Ato ,occupyv a second lposition Y relative to' said outer surface of saidvfilter medium dur-ing -travel Yof said hollow section means in said opposite `direcenvefiao tion, said second position providing a greater spacing between said hollow section means and said outer surface of said lter medium than said first position to thereby reduce wear of said iilter medium during travel of said hollow section means in said opposite direction.

9. In a dust iilter the [combination of a porous flexible ilter medium having an inner surface 4for accumulating solid particles thereon from a dust laden gas and an outer surface on the opposite side of said tilter medium from said inner surface, a reverse jet #cleaning device including hollow section means, means locating said hollow section means in a iirst position relative to said outer surface of said lfilter medium to provide a normal Working position, means for supplying pressurized iluid to said hollow section means, lor-iiice means in said Ahollow section means for directing pressurized fluid toward said outer surface of said lter medium to dislodge said accumulated solids from said inner Surface while said hollow section means is in said normal working position, means for causing7 said hollow section means to move along said outer surface of said lter medium in a rst direction when said hollow section means is in said normal working position, means for causing said hollow section means to move in a second direction which is opposite to said rst direction, and means for causing said hollow section means to occupy a second position relative to said outer surface of said filter medium during travel of said hollow section means in said Second direction, said second position providing a greater spacing between said hollow section means and said outer surface of said lter medium than said first position to thereby reduce wear of said filter medium during travel of said hollow section means in said second direction.

10. A reverse jet cleaning device comprising a carriage including a frame, a plurality of hollow sections for ysubstantially encircling an elongated lter medium, means for mounting said plurality of hollow sections on said Aframe, means forming a part of said mounting means for guiding said hollow sections toward and away `from each other, conduit means in communication with each of said hollow sections for permitting compressed ,air to be supplied thereto, ori'ce means in said hollow sections for directing said compressed air emanating from said sections toward said elongated iilter medium, rst means operatively associated with said hollow sections for providing a iirst spacing therebetween, and second means operatively associated with said hollow sections for providing a second spacing therebetween which is greater than said rst spacing, said rst spacing being utilized when said hollow sections are in a cleaning position and said carriage is being moved in a rst direction, 'and said second spacing being utilized to reduce wear lon said iilter medium when said carriage is moved relative to said el0ngated iilter medium in a second direction which is opposite to said first direction.

References Cited bythe Examiner UNITED STATES PATENTS 5 51 Hersey 55-294 1/ 5 6 Swanson 5 5--294 UNITED? STATES vPATENT oFF-ICE CERTIFICATE oF CORRECTION Patent No 3, l76 ,449 April 6 1965 Carlos S. Schultz et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read es correctedbelow.

for "embodi" read embodi- "is" read in Column 6, Column 8, line Z3, for

Signed and sealed this 24th day of August l965,

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER AI testing Officer Commissioner of Patents 

1. IN A DUST FILTER WHEREIN A POROUS, FLEXIBLE, CYLINDRICAL FILTER MEDIUM IS EMPLOYED FOR ACCUMULATING UPON THE INNER SIDE THEREOF SOLID PARTICLES FROM A DUST-LADEN GAS AND WHEREIN A REVERSE-JET CLEANING DEVICE COMPRISING A PLURALITY OF SEPARATE HOLLOW CURVED SECTIONS MOUNTED ON A CARRIAGE AND SUBSTANTIALLY ENCIRCLING THE FILTER MEDIUM IS EMPLOYED TO DISLOGE THE SOLID PARTICLES FROM THE FILTER MEDIUM BY EHECTING A JET OF PRESSURIZED FLUID FROM WITHOUT TO WITHIN SAID FILTER MEDIUM THROUGH AN ORIFICE IN EACH CURVED SECTION WHILE THE REVERSE-JET CLEANING DEVICE IS RECIPROCATED ALONG THE LENGTH OF THE FILTER MEDIUM, THE IMPROVEMENT COMPRISING MEANS MOUNTED ON THE CARRIAGE FOR MOVING SAID PLURALITY OF CURVED SECTIONS TO A RETRACTED POSITION OUT OF PHYSICAL CONTACT WITH SAID FILTER MEDIUM AND MEANS CONNECTED TO SAID REVERSE-JET CLEANING DEVICE FOR RECIPROCATING SAID REVERSE-JET CLEANING DEVICE WITH A HIGH SPEED "UP" STROKE AND A LOW SPEED "DOWN" STROKE. 